The present invention relates to a thermoforming station including a quick cooling system for quickly cooling the molded products.
The invention also relates to a thermoforming method carried out in the inventive thermoforming station.
More specifically, the present invention relates to a thermoforming station of the type in which a sheet-like plastics material (supplied in plate or coil form) is molded within a bell-shaped molting element arranged at a location opposite to the mold supporting element, thereby said bell element can be closed on the latter.
As is known, in such a thermoforming station, the sheet-like plastics material is brought to the plasticizing temperature thereof and then being locked, at a set molding position, by closing said bell element against the perimetrical edge of the plastics material itself. Then, a vacuum or negative pressure is provided inside said bell element, so as to draw the plastics material into said bell element, to provide the plastics material a pre-stretched ball shape. Under the thus formed ball a mold element is then arranged, while reversing the vacuum direction thereby causing the plastics material to be pressed and adhere to the mold, for the molding operation proper.
Then, the molded plastics material is allowed to cool, the bell element being held in a closed condition to hold the molded article being cooled on the mold. Thus, suitcase shells, motor. vehicle components, refrigerator cells and doors, bath furniture pieces and the like are made.
In this prior molding method, the cooling operation represents the most critical step since the outer surface of the molded articles must be cooled as evenly as possible in order to prevent inner stresses from undesirably deforming the molded article.
More over, the cooling step represents the longest step of the method and, in order to increase the yield, the cooling time should be as short as possible.
On the other hand, the achievement of the above two objectives is hindered by the provision of the mentioned bell element which, as stated, during the cooling period must be held in a closed condition on the plastics material applied on the mold.
For providing a ventilation through the plastics material surface facing the inside of the bell element, the latter is conventionally provided with a plurality of large openings which can be tightly closed during the under vacuum-operations. Inside the bell element is moreover conventionally provided a channel pattern for ejecting pressurized air jets against the surface of the plastics material to be cooled. For this reason, the air outlet openings of the bell element must have a size larger than that of the inlet openings thereby the bell element will be provided with a perforated construction having a lot of smaller and larger openings. The number of these openings, in particular, will depend on the cooling efficiency to be achieved. In this connection, however, it should be apparent that the number of said openings cannot be increased to any desired value, since for a very large number of openings, it would be required to design a lot of expensive sealing elements requiring, furthermore, an intensive maintenance (also considering the comparatively high operating temperature of the bell element).
Accordingly, the aim of the present invention is to provide a thermoforming station of the above mentioned type, which is specifically adapted to cool in a very quick manner the molded plastics material or articles.
Within the scope of the above mentioned aim, a main object of the present invention is to provide such a thermoforming station allowing to carry out therein a molding process requiring a small molding operating time while providing molded articles free of any inner stresses due to a uneven cooling of the surfaces of the molded articles.
Another object of the present invention is to provide such a thermoforming station allowing an efficient circulation of air through the plastics material arranged inside the thermoforming bell element, while allowing said thermoforming bell element to have a comparatively simple construction.
Yet another object of the present invention is to provide a thermoforming station of the above mentioned type which, differently from conventional thermoforming stations requires a very reduced maintenance, while providing a cooling system very resistant against wear and high operating temperatures.
Yet another object of the present invention is to provide such a thermoforming station allowing an improved thermoforming method to be quickly carried out therein.
According to one aspect of the present invention, the above mentioned aim and objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by a thermoforming station for molding a sheet-like plastics material, of the type comprising a mold and a bell element for closing said mold, and being essentially characterized in that said bell element comprises a disassemblable or openable construction adapted to provide a lot of ventilating and cooling openings for ventilating and cooling said plastics material arranged in said thermoforming station.
According to further features of the present invention, said station is moreover provided with driving means for opening said bell element during the cooling of said plastics material and closing said bell element during the hot molding operations of said plastics material. Said driving means are moreover designed for holding said plastics material on said mold, even with the bell element in an open condition for the cooling operations.
The thermoforming station according to the invention is further characterized in that said bell element comprises a side wall and a movable panel which can be closed as a cover on said side wall.
Said driving means for opening and closing said bell element comprise, in turn, a cylinder-piston assembly which is connected, on a side, to said movable panel and, on the other side, to said wall.
According to yet further features of the invention, said thermoforming station comprises moreover side guide elements, preferably of a pinion-rack type, provided for sliding on sliding column and adapted to center the movement of said movable panel and wall of said bell element with respect to one another and to the mold. Means for locking the plastics material on the mold rigid with the edge of said side wall of said bell element, opposite to the engagement edge thereof with said movable panel, are moreover provided.
The thermoforming station according to the present invention is furthermore characterized in that it comprises driving cylinders for raising or opening, in a lockable manner, said wall of said bell element. A fan assembly for providing and orienting air jets inside said bell element, as it is opened by at least one of the mentioned opening driving means is moreover provided.
According to yet further features of the thermoforming station according to the present invention, said thermoforming station is moreover provided with additional ventilating and cooling openings, formed through said side walls of said bell element. On said side wall are moreover provided a plurality of driving cylinders for driving said side wall with respect to said mold, as well as a pressurized air channel arranged inside said bell element and aiding for cooling said plastics material, and a reduction assembly driven by said cylinders and cooperating with the reduction assembly born by said bell element, for holding the plastics material on the mold.
The thermoforming method for thermoforming a sheet-like plastics material by using the inventive thermoforming station, which method also constituted a main aspect of the present invention, is characterized essentially by the fact that said method comprises a step of forming ventilating and cooling slots for said plastics material, by disassembling or opening said bell element, which is held clamped on said plastics material to hold the latter at a fixed position on the mold.
The thermoforming method according to the invention is moreover characterized in that it provides to form said openings by raising or detaching said movable panel from said side wall of said bell element. Further openings are formed by raising or detaching said side wall from said reduction assembly clamped on said plastics material adhering to said mold.
With respect to prior thermoforming stations, the thermoforming station of the invention provides the advantage of allowing a quicker and much more efficient cooling of the molded plastics material. Thus, the overall thermoforming operating time can be reduced up to 50% with respect to a conventional thermoforming time, i.e. the thermoforming time of prior apparatus, to provide an evenly molded product free of any inner stresses due to an excessively quick cooling.
Moreover, the thermoforming station according to the invention, being provided with a bell element free of windows, has a much more simple and reliable construction with comparatively low making costs and maintenance requirements.